Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

Low pressure on high side

I have two three ton carrier units, (they're neighbors), anyway, one unit has low pressure on the high side, about 100 psig. The other unit has real high pressure on the high side, about 300 psig, but its only 75 degrees outside. Both carrier units and neither are heat pumps. Any ideas?

And to add, the suction on the unit with the low high side pressure is high, about 100 psig. And the suction on the unit with the high pressure high side is normal and super heat is correct but the subcooling is way off

Let's start with the low-high side unit...
What is your superheat and sub cooling?
Are your line temps the same (within a couple degrees of each other)?
Is your compressor actually running (pulling amps)?

I've found many compressors that have symptoms similar to this, where the pressures are close, amp draw is half of fla, and the line temps are the same...the cause of this is usually a mechanical failure within the compressor.

Cool Change, are you in this industry as a tech? Or is this DIY? There is nothing in your profile and in this and the other thread you couldn't answer the most basic questions such as Superheat and Subcooling.

Maybe we could have a sticky about posting actual temperatures and pressures when asking for refrigeration advise?

I can see why people give us such incomplete data. If they had collected all the pertinent information, they probably wouldn't need to ask us our diagnosis! With Superheat, subcooling, temperature outside, in return, and supply, we can pretty much figure it out. If we really want to dig deep, give us model and serial,static pressure, wet bulb in and out, flux capacitance, amps, gigawatts... How about the customer's actual complaint once in a while?

Maybe as part of the registration process, they can sign and notarize a pledge to give us some more information!!!

I am a beginner tech in the industry. got a universal with verrrry little experience, so if u wanna work with me I appreciate it. if not, thanks anyway. I left the job and do not remember the data but you bet I will write it all down to report next time.

And to add, the suction on the unit with the low high side pressure is high, about 100 psig. And the suction on the unit with the high pressure high side is normal and super heat is correct but the subcooling is way off

The compressor's not running on the 100 psi low/100 psi high unit and the other is probably overcharged.

I am a beginner tech in the industry. got a universal with verrrry little experience, so if u wanna work with me I appreciate it. if not, thanks anyway. I left the job and do not remember the data but you bet I will write it all down to report next time.

Thank you! Welcome here! We don't really like to give out DIY info. It helps to fill in your profile.

On the unit with equal pressures it sounds like the compressor is not pumping, check amp draw to common winding.

Have you applied for pro membership yet? You need to have 15 posts. All the good tech info is is over in the pro forums. See the bottom of my post for the how to.

DIY tips or answers do leak out but usually only when the right questions are asked. No offense at all, we all started somewhere and are still learning, but sounds like you just have some gauges and an epa card.

So lets start with the unit I'm on right now. I have a superheat of 70 degrees, 30 pounds suction pressure. Head pressure is 155 with -5 degrees subcool. Im drawing 6.7 amps on the compressor. I added two pounds of r22 which brought the stats up to what I am reporting them currently but am reluctant to add more freon till I get some input. T 3.5 ton unithis is a heat pump on a goodman

On the one with low high pressure I chalked it up to compressor going out. I went there to do a prevent maint and found the condensor 1/4 buried in the dirt. Told the homeowner they needed a new compressor very shortly. hope I was right. and think I am but will check the amp draw to the common as suggested. It was drawing 11.4 amps